**4. Conclusion**

In this study, the effects of different environmental and chemical factors on the activity of the enzyme glucose isomerase were tested with the final aim of using this enzyme for the conversion of fructose to glucose present in stuck wine fermentations.

To conclude, 0.5% w/v glucose formation from 1% w/v fructose took place in synthetic medium containing 13% v/v ethanol and 1% v/v glycerol at pH 3.3 and at temperatures of 60 or 30°C in approximately 48 hours. However, the glucose formation did not take place in synthetic medium if there was 0.3% w/v tartaric acid at pH 3.55, whereas glucose was formed at pH 6.33. In the original wine medium with dilution effect and at pH values equal or higher than 6, glucose was formed from fructose whether there was tartaric acid or not. Since dilution and increasing the pH of wine cannot be applicable, other ways to employ this enzyme to prevent stuck fermentation should be tried.

In final words, we can mention some methods that can be employed for stuck fermentations. A membrane system can be used for separating acetic acid from the wine medium [16]. This may increase glucose formation from fructose by using glucose isomerase. If a low pH resistant glucose isomerase can be searched and found, thanks to this enzyme, fructose be converted to glucose and stuck fermentation may be prevented. Finally, though not related to glucose isomerase, different yeast strains may be employed. The yeast strains usually employed in enology have glucophilic characters that prefer glucose against fructose. Fructophilic yeast strains, even if not employed at the start of the fermentations, may be added to stuck fermentations and may help consume the residual fructose in the medium.

*Grapes and Wine*
